1. Field of the Invention
The present invention is directed to a method for producing a laterally limited single-crystal region in a substrate using selective epitaxy. Such a region may be the collector of a bipolar transistor or the action region of a MOS transistor, and thus the invention is also directed to methods for manufacturing bipolar and/or MOS transistors.
2. Description of the Prior Art
Selective epitaxy is increasingly employed in semiconductor technology in the production of electrically active regions is substrate. Before the selective epitaxy, a mask structure having an opening wherein the surface of the substrate is exposed is produced on the surface of a substrate. The exposed surface of the substrate is composed of a single-crystal semiconductor, particularly silicon. The mask structure is selected such that single-crystal semiconductor material grows in the selective epitaxy proceeding from the exposed surface of the substrate and such that no semiconductor material grows on the surface of the mask structure. A single-crystal region that is completely surrounded by the mask structure arises in this way. The mask structure is essentially composed of insulating material and serves the purpose of insulating the active region. In selective epitaxy, the electrically active regions are grown in openings of an insulating layer.
In conventional insulation methods such as, for example, LOCOS or a trench, by contrast, the regions required for insulation are "dielectrically filled," for example with oxide.
It is known from J. Borland et al., Solid State Techn., January 1990, pages 73-78 to produce a collector, base and/or emitter in bipolar technology on the basis of selective epitaxy. Selective epitaxy is also employed in CMOS technology. Thus, for example, a CMOS well (see, for example, J. Manoliu et al., IEDM Digest, 1987, pages 20-23) or source and drain (see, for example, European Application 0 268 941 corresponding to U.S. Pat. No. 4,885,617) can be filled by selective epitaxy.
Tests have shown, however, that diodes produced with selective epitaxy are inferior to conventionally manufactured diodes, for example, with LOCOS insulation, with respect to leakage currents (see A. Stivers et al., Proc. of 19th Int. Conf. on CVD, October 1987, Honolulu pages 389-397). These leakage currents are associated with sidewall defects. Sidewall defects are crystal faults that arise along the edges of the active epitaxial layer. Since the semiconductor material, for example silicon, grows epitaxially in the opening of the mask structure which, for example, is composed of SiO.sub.2 or Si.sub.3 N.sub.4 in selective epitaxy, and the sidewalls of the opening composed of dielectric material represent a source of crystal faults, crystal faults comprising the aforementioned sidewall defects arise in this region during the selective deposition.
In order to avoid the sidewall defects in selective epitaxy, it is known to line the dielectric sidewalls with polysilicon or nitride (see, for example, A. Stivers et al., Proc. of 10th Int. Conf. on CVD, October 1987, Honolulu, pages 389-397). Further, C. S. Pai et al., J. Electrochem. Soc., Vol. 137, 1990, pages 971-976 discloses that the appearance of sidewall defects is minimized under specific epitaxy conditions. It is also known from C. S. Pai et al., J. Electrochem. Soc., Vol. 137 1990, pages 971-976 to reduce the defects by aligning the edges of the active transistor regions along (100) crystal directions in a silicon substrate. Substrates wherein the edges of the active transistor regions proceed along (110) directions are, however, usually employed. A rotation of the transistor structures by 45.degree. makes it possible to employ the standard (110) silicon substrates and to nonetheless achieve a reduction in the level of defects.